Heretofore, various arrangements have been proposed for automatically changing the speed of a two-speed fan motor in a vacuum cleaner in response to certain varying conditions, but none has provided an automatic control which results in a substantially constant air flow under all conditions within, of course, the limits of the capabilities of the system. Thus, in U.S. Pat. No. 2,789,660 of Apr. 23, 1952, there is disclosed an arrangement whereby the speed of a two-speed fan motor is increased in a single step in response to a predetermined increase in pressure drop of air through the dust bag, but the control in this patent is not responsive to change in air flow conditions at other points in the system, such as at the nozzle. In U.S. Pat. No. 3,069,068 of Dec. 18, 1962, there is disclosed a vacuum cleaner having a two-speed fan motor, the speed of which is increased in a single step in response to a predetermined increase in pressure difference across the fan. In neither of these patents is the system described capable of maintaining a substantially constant air flow by utilizing a pressure variation within the vacuum cleaner system and atmospheric pressure.